Although a growing body of evidence has suggested that sialoglycoconjugates may play an important role in the formation and maintenance of the myelin sheath, information about their metabolism and regulation in myelin and oligodendroglial cells is still scanty. The investigators have studied neuraminidase activities in the central nervous system and demonstrated the presence of neuraminidase activities intrinsic to myelin and oligodendroglial cells. To elucidate the functional roles of neuraminidase in myelin and oligodendroglial cells, the following specific aims are proposed: (1) purification and characterization of myelin-associated neuraminidase, (2) localization of the enzyme, (3) regulatory mechanisms for developmental expression of the enzyme activities in myelin and oligodendroglial cells, and (4) functional roles of myelin-associated neuraminidase. To achieve these goals, the investigators will first purify myelin-associated neuraminidase to homogeneity from rat brain. The biochemical and kinetic properties of the enzyme will be examined and compared with those of neuraminidase activities in microsomes. Specific antibodies against the enzyme will be prepared to examine the localization of the enzyme using immunocytochemical and immunoblotting techniques. In order to examine whether the neuraminidase activities in myelin and oligodendroglial cells are regulated at the mRNA level, the developmental expression of mRNA coding for myelin-associated neuraminidase will be examined using a specific cDNA probe prepared with mRNA of rat oligodendroglial cells.The mechanism of the developmental changes in the activity of the myelin enzyme will also be investigated by analyzing the amounts, integrity, and micro- environment of the enzyme during development. To examine the metabolic role of myelin-associated neuraminidase, developmental changes in the composition of sialoglycoconjugates in myelin and oligodendroglial cells will be examined in relation to the neuraminidase activities directed toward endogenous sialoglycoconjugates as well as exogenous substrates.The possibility that myelin-associated neuraminidase may function as an adhesion molecule will be investigated using different types of binding experiments and cell culture systems. The achievement of these specific aims should provide vital information concerning the role of myelin-associated neuraminidase in the formation and maintenance of the myelin sheath.